Thursday, 8 August 2013

Human Evolution In Progress

Why We "Got Milk": Scientific American

An excellent article on the human lactose tolerance genetic mutation and how it has played an important part in human success. I have blogged about this before in Lactose Tolerance And Creation 'Science' so I won't go into much detail beyond covering the main facts.

Human babies 'normally' (i.e. those who have the normal gene for lactose intolerance) breast-feed for about 18 months to 2 years then develop a distaste for milk due to losing the ability to digest the sugar (lactose) in it. They lose this ability because they stop producing the enzyme lactase which digests it. This natural mechanism ensures babies don't continue breast-feeding indefinitely and are forced to change to an adult diet.

Breast-feeding is a natural contraceptive because the act of suckling stimulates the mother to produce a hormone which inhibits ovulation so, when the baby stops breast-feeding the mother can become pregnant again. Through evolution a balance had been established so a baby gets the mother's attention for the first couple of years, then she can reproduce again. Meanwhile, if the baby dies, the mother can become pregnant again more quickly. This strategy produced most descendants in the long run so it became the normal mechanism.

However, when humans began to domesticate animals, for food at first (hunter-gatherers don't hunt large mammals to milk them but to eat them) they would quite soon have discovered they needed to limit the herd size in some way, presumably by killing the newborn calves, lambs, kids, etc. They would soon have discovered they had a plentiful supply of spare milk going to waste. What would be more natural than to supplement babies' diets with sheep, cow or goat milk?

Now it became possible to wean babies off the breast and onto other milk. It also meant that others could feed baby - older siblings, fathers, grandparents, etc - so the mother's natural contraceptive was removed and more babies could be produced. Additionally, children could benefit from this extra milk and those who had the lactose tolerance mutation (which should really be called the lactase persistence gene) could continue to reap this extra benefit into adult life, so they too could produce more children (who also carried the mutation), so the lactose persistence gene would have had a very significant advantage in the presence of milk-producing domesticated animals.

But herding domestic animals is only possible in areas of the world where there is all-year grazing and the animals are not predated by, for example, the parasite carried by tsetse flies. There is no advantage in other areas; in fact, it has the same disadvantage which prevented it evolving before animal domestication in the first place.

Those are the main points in the evolution of lactase persistence. For more detail see the blog linked to above.

So what lessons are there from this and the above article, especially, creationists?
  1. This enormous advantage was produced by a mutation, giving the lie to claims that mutations are always harmful.
  2. This mutation involved no change in the amount of information in the genome. It was a simple substitution of one nucleotide - cytosine for another - thymine. What changed was the meaning of the information. If you don't know the difference, read Evolution - The Meaning of Information. This gives the lie to claims that evolution is impossible because new information can't be created (due to some misrepresentation or misapplication of the Laws of Thermodynamics).
  3. The meaning of the information was determined by the environmental context. It would have been meaningless in the absence of pastoralist cultures which included domestic animals. This shows how the meaning of information is determined by the environment, so evolution can be driven by environment change just as much as by genetic change.
  4. The spread of dairy farming illustrates how recent human evolution has been influenced by memes and is an example of gene-meme co-evolution, showing how replicators responding to natural selection pressure form alliances with other replicators without regard to the nature of those replicators. Once humans evolved intelligence and the means to replicate ideas (memes) and pass them on to descendants, it became inevitable that they would also play a part in human evolution.
  5. There is no such thing as more or less evolved because evolution is always tending to fit a species for its environment. In a wide-spread species like Homo sapiens we would expect evolution to be different in different environments and this is exactly what we see with lactase persistence. Lactose tolerant and lactose intolerant populations are no more or less evolved than the other. They are both equally fitted to their cultural, geographical and biological environments. Incidentally, this also holds true for every other living species. Everything has been evolving for exactly the same amount of time and everything is at the pinnacle of it's own evolution. The only pinnacle of evolution that humans occupy is that of human evolution.

A glance at the map above will also show how beneficial genes flow into the genepool and spread into adjacent populations. It is not necessary for populations to migrate for genes to spread. Once a beneficial gene has been concentrated in a population by giving its carriers an advantage and so moving up the improbability gradient, that population can act as a reservoir from which the gene can spread. However, as it comes up against populations in environments in which its meaning no longer applies, there is nothing to keep it concentrated, so it can be diluted with no loss of advantage to the carriers.

The lactase persistence gene distribution has nothing to do with racial, linguistic, religious or political boundaries and has no regard to socio-economic status.

We can see in this map that the lactase persistence genes predominate in areas suitable for dairy farming and the lactase cessation gene predominates where dairy farming is impossible. In fact, in central North Africa we can see a reverse effect, as the lactase cessation gene flows out from a reservoir of its own from a population in which the persistence mutation is almost absent.

This is human evolution in progress and everything about it is consistent with neo-Darwinian gene-centred evolution.

Why would an intelligent designer design the distribution of this gene and its non-mutant form so they look like concentration gradients from centres of high incidence and distribution patterns that look for all the world like the product of gene-meme co-evolution mediated by the varying geographical and biological environments?

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1 comment :

  1. Your blogs and its stuff magnetize me to return again n again. evolution proof

    ReplyDelete

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